Report of Experiments on the Growth of Wheat. 
491 
carbon from atmospheric sources, than when it was grown on the 
practically exhausted unmanured land. 
6. Nitrogenous manures alone, increased the produce A r ery 
considerably for many years in succession ; hence, the soil in its 
practically exhausted condition was relatively much richer in 
available mineral constituents, than in available nitrogen. 
7. The largest crops were obtained when mineral and nitro- 
genous manures were employed together ; and it was by such 
mixtures, even though they supplied no silica (nor carbon), that 
the produce by farmyard manure was far exceeded, although the 
latter supplied, not only both silica and carbon, but all other con- 
stituents in larger quantity than they were removed in the crops. 
The question arises — Will any conclusions drawn from these 
results regarding the character of the exhaustion induced by a 
course of cropping in this particular soil, and consequently 
regarding the description of manure required before it will again 
produce full crops of wheat, be at all applicable to any other soil, 
or to soils generally ? 
Baron Liebig, although he profusely illustrates his own views by 
reference to field experiments, and even to isolated results of our 
own, if by unfair representation they can be made to serve his 
purpose, and although it is*doubtless by the evidence of such 
experiments that he has been led to his present, and on many 
points greatly amended, views, at the same time denies the 
utility of field experiments generally, and of our own in parti- 
cular, as a basis of deduction regarding even a neighbouring 
field, and, still more, a field in any other locality. Other autho- 
rities look at field experiments in a very different light. Only 
a few weeks since, in a lecture delivered before the members of 
the Highland and Agricultural Society of Scotland, at Stirling, 
Professor Anderson took as his subject the importance and 
the best mode of promoting field as well as other experiments 
in connexion with agriculture. 
With regard to the particular soil upon which the experiments 
which form the 'subject of this iteport were made, Baron Liebig, 
according to the exigency of his argument, has maintained alter- 
nately that it was so rich, and so poor, in mineral constituents, 
that it was utterly unfit for the purposes of our investigation. To 
aid the judgment of those who may wish to consider the subject 
in the spirit of candour proper to an important practical and 
scientific inquiry, it may be well to indicate how far the results, 
briefly stated above, are consistent with those obtained in direct 
experiments in an adjoining field, and on soils of very different 
descriptions in other localities, and also how far they are con- 
sistent with the common experience of practical agriculture in 
this country. 
